Grading System

MEDIUM-HARD · C · 3000ms

At the end of the semester, the library wants Rina's kiosk to convert numeric exam scores into letter grades for the results board. Given a score 0-100, print the grade: "A" for ≥80, "B" for ≥60, "C" for ≥40, "F" otherwise.

Input

One integer score.

Output

One of A, B, C, F.

Constraints

0 ≤ score ≤ 100

Sample Input

72

Sample Output

B
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Grading System · DIU ContestHub